Manufacture of gasoline



March 2, 19.43. F. E. FREY MANUFACTURE OF GASOLINE Filed Aug. 26, 1940 BOlVNOIlDV HOLYUOHV HQLVNBSOHGAHBO INVENTOR I FREDERICK E. FREY BY Patented Mar. 2, 1943 MANUFACTURE OF GASOLINE Frederick E. Frey, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Application August 26, 1940, Serial No. 354,299

* 1 Claims.

This invention relates to a process of manufacturing motor fuel, and more particularly to the utilizing of parafilns having two to four carbon' atoms per molecule for'the manufacture of gasoline having desirable volatility and other characteristics.

One modification of the invention comprises, in combination, the following steps; Converting a part of the paraifins in a feed stock comprising parafiins having two to four carbon atoms per molecule into unsaturated hydrocarbons of the same or a smaller number of carbon atoms per molecule; subjecting at least a part of the hydrocarbons having two to four carbon atoms per molecule in the resulting mixture to a first set of conditions favoring union of the unsaturated hydrocarbons with paraflins to form hydrocarbons boiling in the gasoline range; subjecting at least a part of the unreacted hydrocarbons having two to four carbon atoms per molecule to a second set of conditions favoring union of the unsaturated hydrocarbons with paraflins to form hydrocarbons boiling in the gasoline range; and returning at least a part of the residual hydrocarbons having two to four carbon atoms per molecule to the step for converting parafiins into unsaturated hydrocarbons.

An object of a modification of the invention is to decrease the volatility oi natural-gasoline hydrocarbons comprising isoparafiins having four to seven carbon atoms per molecule.

Other objects and advantages of the invention 1 will be obvious to those skilled in the art from the accompanying disclosure and discussion.

' The invention will be understood readily from the following description of a preferred embodiment thereof and from the accompanying drawing, which shows a flow-diagram for a preferred mode of operation.

A feed stock comprising chiefly paraflins having at least two and not more than four carbon atoms per molecule and preferably having a substantial content of isobutane enters the system through inlet I having control-valve 2. It passes into dehydrogenator 3, in which a part of the paraifins are. converted into unsaturated hydrocarbons, primarily olefins, having the same or a smaller number of carbon atoms per molecule. a

- For example, the dehydrogenator may be'a crack- I have found that the union of unsaturated hydrocarbons having three and four carbon atoms per molecule with paraffins to form hydrocarbons boiling in the gasoline range usually occurs most efliciently under such conditions that the union of ethylene with parafilns occurs only to a relatively small extent, and that this is especially true when the reaction is promoted by a catalyst. I have found it advantageous to effect the union of unsaturated hydrocarbons having two and more carbon atoms per molecule and in a mixture with paraflins in two steps, first under a first set of conditions that promote efilcient union of olefins heavier than ethylene, and other unsaturates, with paraflins, and subsequently subject- 'ing unreacted hydrocarbons to a second set of conditions that promote efiicient union of ethylene with paraflins.

An object of this invention is to provide a process of manufacturing motor fuel from lighter hydrocarbons.

Another object is to utilize parafflns having two to four carbon atoms per molecule for the manufacture of gasoline.

Another object is, in effecting the union of a mixture of unsaturated hydrocarbons having two to four carbon atoms per molecule with parafiins to form hydrocarbons boiling in the gasoline range, to isolate the uniting of ethylene with paraflins and to effect it under conditions that promote it efllciently.

Another object, is to manufacture gasoline having desired volatility characteristics.

'ing coil in which the paraflins are cracked thermally under known conditions into unsaturated hydrocarbons, or it may be a catalytic dehydrogenator in which one or more of the known catalysts for cracking or for dehydrogenating paraffins into unsaturated hydrocarbons is used under dehydrogenating conditions.

From the dehydrogenator 3 the products and unreacted hydrocarbons may be passed through valve 4 and conduit 5 into fractionator B, which serves chiefly to remove methane and hydrogen; these are withdrawn as a light-gas fraction through valve 1 and outlet 8. A hydrocarbon fraction which has been substantially freed from methane and hydrogen is passed through valve 9 and conduit i0 into alkylator II. V

If desired, under some conditions of operation, at least part of the eiiluent from dehydrogenator 3 may be passed through valve I2 and by-pass conduit l3 directly to conduit l0 and thence to alkylator ll without undergoing fractionation in iractionator 6.

In alkylator II, the hydrocarbons are subjected to conditions favoring union of parafllns, especially isoparafiins, with low boiling unsaturated hydrocarbons such as olefins having three and more carbon atoms per molecule to form heavier, predominantly parafiinic, hydrocarbons boiling. chiefly inthe motor fuel or gasoline I range. A minor proportion of the oleflns appear to undergo polymerization, especially if the concentration of isoparafiins is not considerably in excess of that of the olefins having three and four carbon atoms per molecule. Some other sidehigher-boiling hydrocarbons, although they should not be so mild that any substantial proportion of acetylenes and dioleiins present can escape reaction. For example, the conditions may comprise the presence of a known alkylation catalyst that facilitates the union of gaseous oleflns, especially propylene and butylenes, with paraflins. Among such catalysts are aluminum and zinc chlorides and bromides, mixed salts of aluminum chloride or bromide with various metal chlorides and bromides, such as an equimolar mixture of sodium and aluminum chlorides (sodium chloroaluminate), boron fluoride, zirconium chloride, and the like, concentrated sulfuric acid, and concentrated hydrofluoric acid. Of these catalysts, concentrated sulfuric acid or hydrofluoric acid is preferred, when theconcentration of isoparaffins is relatively high, as they appear to promote the union of propylene and butylenes with lsoparaflins more selectively than other known alkylation catalysts, to produce highly desirable products, while when there is little if any concentration of isoparaflins and normal paramns are to be reacted predominanty, aluminum chloride or bromide, sodium chloroaluminate, and other similar catalysts are to be preferred. The concentration of the sulfuric acid preferably should be maintained within the range of about 90 to 102 per cent, advantageously above about 96 per cent, because the higher strengths of acid promote the reaction of the oleflns, especially propylene,.more than the lower strengths. Strengths outside of the range given, down to about 80 per cent and up to about 105 per cent, may be employed;

however, strengths so low as to promote exces- .sive olefin polymerization and so high as to cause. excessive consumption of ethylene and/or excessive reduction of the acid should be avoided. The sulfuric acid catalyst may be used at temperatures in the range of to 125 F., preferably at about 30-to 76 F. It, or any other mobile alkylation catalyst, may be fed to alkylator ll through inlet l4 having control-valve l5; it then is mixed intimately with the hydrocarbons carried to the alkylator by conduit III. as by vigorous mechanical stirring. If hydrofluoric acid is used its concentration is preferably greater than 90 per cent, and often .substantially anhydrous hydrofluoricacid will be found most desirable. Other reaction conditions will be substantially the same as those discussed for concentrated sulfuric acid.

The reaction mixture in alkylator ll, especially if sulfuric acid is used as the catalyst, must i have a substantial content of isopar'aflins, preferably in excess of two molecules of isoparaflins for each molecule of olefin. To aid in maintaining a suitable concentration of isoparafilns, a feed stock comprising isoparaflins having between four and seven carbon atoms per 'molecule, inclusive, may be added, as through inlet 59 having control-valve 60 and thence through conduits 56 and I0 to alkylator ll.

After substantially all of the butylenes and at least the major part of the propylene have reacted in alkylator H, the mixture of hydrocarbons and alkylation catalyst, if a fluid or mobile alkylation catalyst is used, is passed through valve l6 and conduit [1 to separator l8, in which the hydrocarbons and the catalyst are separated. If sulfuric acid is used as the alkylation catalyst, separation is effected simply by settling into two layers by gravity or, if desired, by centrifuging; for some mobile alkylation catalysts, other steps, such as filtration, may be necessary. The alkylation catalyst may be withdrawn through valve I 9 and outlet 20, and thence it may be subjected to a process of reclamation,

5 if desired; or, alternatively, it-may be returned,

partly or entirely, as is desired or as trial indicates is desirable, to alkylator H through valve 2| and conduit 22. The hydrocarbons are passed through valve 23 and conduit 24 to the fractionator 25.

If a fixed or an immobilealkylation catalyst is used in alkylator II, the separator l8 and its accompanying contiguous conduits and valves,

Infractionator 25 the hydrocarbons are frac -v tionated into a motor fuel fraction, which is withdrawn through valve 21 and outlet 28; into an oil fraction, which is withdrawn through valve 25 29 andoutlet 30; and into a light-hydrocarbon fraction comprising chiefly hydrocarbons havingtwo to four carbon atoms per molecule, which is passed through valve 3! and conduit 32 to the pump 33. Optionally, if desired, the light- 30 hydrocarbon fraction may comprise also at least part of the lower-boiling motor fuel hydrocarbons, such as hydrocarbons having five to seven carbon atoms per molecule. The pump 33 sends the hydrocarbons at high pressure through one 35 or more valves, such as valves 34, 35, and 36, 1

and the corresponding branch-conduits I1, 38, and 39, into alkylator 40, wherein they are subjected to a second set of conditions favoring union of oleflns, especially ethylene, with paraflins to form hydrocarbons boiling in the motor fuel range. Any light gases which may at times be present, such as hydrogen or methane, may be passed from the system'through the valved conduit 25A at the top of fractionator 25.

If desired, at least part of the ethylene in the mixture of gaseous effluent from dehydrogenator 3 may be by-passed around alkylator ll, separato'r l8, and fractionator 20 by operating fractionator 6 in such a way that an ethylene-containing fraction, which may also contain, if desired, at least part of the propylene, may be passed through valve 4| and conduits 42 and 42 directly to pump 33 and thence to alkylator 4|. In alkylator 40, the ethylene is caused to react "with paraflins to form higher-boiling hydrocarpresent react similarly. Although many of the known catalytic alkylation processes are suitable for effecting this reaction, under more or less drastic conditions, it is preferred to use a thermal alkylation process, or modification thereof, such as is disclosed-in the Frey patents, U. S. 2,002,394 or U. S. 2,104,296, or in the copending applications Serial Numbers 82,954, now U. S. Patent 2,270,700, granted January 20, 194 2, or 122,658, now U. 8. Patent 2,266,019, granted December 16, 1941. In such a process the hydrocarbons in alkylator 40 are maintained at a temperature within the range of about 750 to 1100 F. and under a pressure in excess of about 500 pounds per square inch, preferably in the range of 2,000 to 10,000 or more pounds per square inch, and the content of added oleflns in the reaction mixture is maintained at not more than about 10 per cent by weight of the hydrocarbons therein, as by controlled addition of bons; any oleflns heavier than ethylene'that are olefin-containing streams at aplurality of points. By such process the ethylene, together with any heavier oleflns that may be present, is caused to unite with paraflins, both normal paraflins and isoparaflins, some of which may be introduced into alkylator 40 through conduit and pump 54, to form paraflinic hydrocarbons boiling chiefly in the gasoline range, such as pentanes, hexanes, heptanes, octanes, and the like hydrocarbons of higher molecular weight.

After the alkylation reaction occurring in elkylator 40 is substantially complete, the hydrocarbons are passed through valve 43 and conduit 44 into fractionator 45, in which they are sepadrawn through valve 46 and outlet 41; into a heavier fraction, which is withdrawn through valve 48 and outlet 49; and into one or two, as

desired, light-hydrocarbon fractions, whichpass to either one or both of the units consisting of dehydrogenator 3 and alkylator 40 throughconduits 50 and/or 51 in proportions controlled by valves 52 and 53, respectively. Light, undesired gases may be removed through the valved conduit 45A at the top of the fractionator 45. The stream rated into a motor fuel fraction, which is with from fractionator 45 through valve 55 and conduits 56 and III to alkylator ll, wherein the parafllns, particularly the isoparafiins, may be alkylated with oletlns, mainly propylene and butylenes, into higher-boiling gasoline hydrocarbons. Simi larly, still further advantageous control of the volatility of the motor fuel product may b obtained, if desired, by passing a fraction containing at least part of the lower-boiling hydrocarbons from fractionator 35 through valve 51 and conduits 58, 56, and Ill to alkylator i I wherein the parafllns may be transformed into higherboiling motor-fuel hydrocarbons by being alkylated with olefins; sucha fraction advantageously may contain hydrocarbons having between four and seven carbon atoms per molecule.

In a modification of the present process, a feedstock comprising isoparafiins having between four passing through conduit 5| to alkylator 40, which is raised to a suitable high pressure by means of pump 54, may comprise any selected part or all of the lower-boiling hydrocarbons present in the mixture in fractionator 45, not only those boiling below the gasoline range but also, if desired, the lower-boiling gasoline boiling range hydrocarbons, such as those having five to seven carbon atoms per molecule; the composition of this stream 1s controlled or varied at will between wide limits by the manner of operation of fractionator 45, and this stream preferably should comprise mainly paraflins having between four and seven carbon atoms per molecule. Similarly, the composition of the stream passing through conduit 50 d hydrogenator 3 may be varied within wide l1m1ts by the manner of operation of fractionator 45;

although this stream generally comprises mainly hydrocarbons having two to four carbon atoms per molecule, it may also comprise, if desired, any selected part or all of the lower-boiling motor fuel hydrocarbons that have up to seven. carbon atoms per molecule, advantageously the pentanes. The principal low molecular weight reaction products of ethylene and such hydrocarbons as propane or normal butane are isoparafiins, such as 2-methy1 butane (isopentane) and 3-methyl pentane, which may be readily reacted with propylene or butylenes, or thelike, in .the presence of co ncentr ated sulfuric acid to produce less volatile compounds. The separating means represented by fractionator 45 may be so operated as to separatea' fraction rich in. such alight isoparaflln, and this fraction may be passed directly to alkylator .Il through-conduit 50 and through conduit 04 andvalve BSto-conduit IHI, with suitable control ofvalve 63.

By control of the proportions'oi"lower boiling "hydrocarbons included in either one or both of the'streamspassing'through conduits 50 and 5| from fractionator 45, the volatility of a motor fuel product may be varied within wide limits, for the lower-boiling motor fuel hydrocarbons so included are subjected to subsequent conditions favoring transformation of them into higher-boiling motor fuel hydrocarbons by alkylation with oleflns Further advantageous control of the volatility of the motor fuel product may be obtained, if desired, by passing at least part of the lower-boiling motor fuel hydrocarbons as a separate fraction v and seven carbon atoms per molecule is fed into the process, as through inlet 59 having control valve Bil-and thence through conduits 56 and ID to alkylator l I, wherein at least part of the isoparaflins are alkylated with olefins into higher-boiling motor fuel hydrocarbons. Similarly, a feedstock comprising parafins, preferably isoparaiilns, having between four and seven carbon atoms per molecule, may be fed to alkylator ,40, asthrough inlet 6! having control-valve 62 and thence through conduit 5| and pump 54. Suitable feedstocks for introduction through inlet 59 and/or inlet BI are light natural-gasoline fractions, casinghead gasolines, unreacted hydrocarbons from a process of partial dehydrogenation, and the like. which advantage'ously'comprise isoparafl-lns having between four and seven carbon atoms per molecule.

The motor fuel fractions efiluent from fractionators 25 and may be used as such separately,

or they may be blended together in any desired proportion. It is advantageous to control the conditions of operation of the various units in the process in such a manner that the motor fuel stock efliuent from fractionator 25 has a lower volatility than that of the motor fuel stock effluent from fractionator 45, and generally such a, result is an inherent part of my process; and a motor fuel of any desired intermediate volatility may be obtained by blending the two motor fuels stocks in proper proportions.

In place of charginggaseous paraffin hydrocarbons through conduit l to the dehydrogenating v or cracking apparatus 3, a relatively heavy oil may becharged', and the apparatus 3 will then be operated as an oil cracking step. ns-another modification. this apparatus may beoperated for reforming naphtha, or'as. a gas reversion operation. .In such acase appreciable amounts of normallyzgaseous. and/or low boiling liquid hydrocarbons,'both parafllns and ,olefins, will be produced, and a mixture comprising these can be charged to the allcvlator ll through valve! and ,condu'itgimfrom fractionator 6, as has previously beendiscussed in connection with the operation of the apparatus: for the dehydrogenation of gaseous paramns. Also, gaseous paraflins may be converted by high or low pressure thermal unitary conversion to low-boiling liquid hydrocarbons in unit 3. With sucha modification unreacted propane and/or butane may be separated from the effluent of the catalytic alkylation step through conduit 25A and recirculated to the conversion unit 3 through conduit l. erations, heavier hydrocarbons, comprising tor fuel and heavier oils, may be removed from fractionator 8 through valved conduit 61. Alter- With suchop-' animal.

natively, an oil cracking or a naphtha reforming or similar operation may be carried out in apparatus not shown, anda desired charge stock for the alkylator II can be introducedthrough conduits-59, 58 and I0. With this latter modification, dehydrogenator 3 and fractionator 6 may be completely eliminated from the system, or may be used to treat only hydrocarbons recycled through conduit. and valve 63 to conduit I.

It is to be understood, of course, that various parts, or units, of equipment have been shown diagrammatically, and that in any commercial plant there will need to be numerous heating units for the dehydrogenators, fraotionators, alkylators, etc., cooling units, surge tanks, pumps, etc., and-that each fractionator, although shown as a single unit, will generally comprise two or more fractionating columns with suitable reflux equipment, separators, and the like. Any particular modification and installation will have its own particular requirements in this respect, which in any case, can be readily supplied and equipped by one skilled in the art without departing from the spirit of the teachings of the present disclosure.

The following example is given purely for the purpose of illustrating one of the many possible modes of operation of the process; it is not necessarily to be taken as establishing limitations of the process.

Example A feed stock comprising chiefly parafilns having two to four carbon atoms per molecule and containing 35 per cent isobutane is cracked to the extent of 15 to 20 per cent. After being freed from methane and hydrogen by fractional distillation, the resulting mixture, which contains butylenes, propylene, ethylene, and more than 20 per cent isobutane, is subjected at room temperature to the action of sulfuric acidhaving an initial strength of about 100 and a final strength of about 90 per cent H2804 by weight. The acid and hydrocarbons are agitated vigorously. After the major part of the propyleneand substantially all of the butylenes have reacted, the mixture of hydrocarbons and acid is separated into two layers by settling. The upper or hydrocarbon layer is fractionated, and gasoline and heavier hydrocarbons are withdrawn; th residual hydrocarbons are pumped into a thermal alkylation unit of the type disclosed in U. S. 2,002,394, wherein they are subjected to a temperature between about 750 and 1000 F. and a pressure in excess of 1000 pounds per square inch for a time sufficient for the major part of the ethylene and .substantially all of the propylene to unite with parafiins. The resultant gasoline and heavier hydrocarbons are separated by fractional distil- .lation and withdrawn, and the residual hydrocarbons are recycled to the cracking unit. By this operation, two gasolines of somewhat difierent properties are obtained: That from the sulfuricacid alkylator comprises predominantly heptanes and octanes, and that from the thermal alkylator comprises predominantly pentanes and hexanes. When these two stocks are blended the volatility characteristics of the one balance and supplement the volatility characteristics of the other to produce a single, well-balanced gasoline.

Many modifications of the process will be obvious to those skilled in the art. For example, the

. feed stock going to the dehydrogenation step may comprise the hydrocarbons, including olefins,

having two to four carbon atoms per molecule alytic cracking of heavy liquid hydrocarbons,

manufacture of gasoline by concurrent thermal cracking and thermal polymerization of gaseous hydrocarbons, and the like. If a feed stock containing olefins is used. the dehydrogenation unit advantageously may be made of a capacity smaller than that necessary if the feed stock consists substantially entirely of paraflins. As another example, the feedstock tothe dehydrogenation step may have a substantial content of hydrocarbons having more than four carbon atoms per molecule, advantageously five-carbon hydrocarbons, whereupon the volatility of the gasoline produced is relatively substantially smaller because of the formation of five-carbon olefins that alkylate with paraihns, including isopentane.

In view of the many possible modifications of 'unduly by the foregoing specification and example, but it should be understood to be extensive in spirit and equivalents within the scope of the claims.

' I claim:

1. In a process for producing normally liquid hydrocarbons in the'rnotor fuel ooiling range from lighter hydrocarbons, the steps which comprise subjecting a hydrocarbon mixture contain ing ethylene and heavier olefin hydrocarbons and also propane and heavier paraflin hydrocarbons ma first alkylation step to a reaction temperature and pressure in the presence of an alkylation catalyst for a period of time sufiicient to effect a union of said heavier olefins with parafiins to produce an optimum yield of paraflin hydrocarbons in the motor fuel boiling range, removing from the effluent a hydrocarbon mixture comprising normally liquid hydrocarbons so produced. separating also from the effluent a hydrocarbon mixture containing ethylene and light parafilns having at least three carbon atoms per molecule,

subjecting said last-mentioned hydrocarbon mixture in a second alkylation step to alkylation conditions including a reaction temperature between 750 and 1100 F. under a pressure in excess of 500 pounds per square inch in the absence of a catalyst for a period of time sufiicient to effect a union of ethylene with parafiins to produce an optimum yield of paraflins in the motor fuel boiling range, separating from the eiliuent a fraction comprising hydrocarbons in the motor fuel boiling range so produced, and also separating from said effluent a hydrocarbon fraction containing normally liquid hydrocarbons of not more than seven carbon atoms per molecule and returning said 1'. action to said second alkylation step.

2. A process of manufacturing gasoline from a feed stock comprising paraffins having two to jecting at least part of the hydrocarbons having two to four carbon atoms per molecule in the resulting mixture to the actionof sulfuric acid having a strength of from to per cent and a temperature within the range of 0 to F. for a time suiiicient to effect union of the major part of the unsaturated hydrocarbons having three and four carbon atoms per molecule with parafiins to form hydrocarbons boiling in the asoline range, subjecting at least. part of #52 unreacted hydrocarbons having two to four carbon atoms per molecule to the action of thermalalkylation conditions comprising a temperature within the range of 750 to 1100 F. and a pressure in excess of about 1000 pounds per square inch for a time sufflcient for substantially all of the unsaturated hydrocarbons having two to four carbon atoms per molecule to unite with parafiins to form hydrocarbons boiling in the gasoline Y range, recycling at least part of the hydrocarbons efliuent from-said thermal-alkylation conditions and having two to seven carbon atoms to the said thermal-alkylation conditions, and returnin at least part of the residual hydrocarbons having two to four carbon atoms per molecule to the step for converting parafilns into unsaturated hydrocarbons.

3. A process of manufacturing gasoline from a feed stock comprising parafiins having two to four carbon atoms per molecule, which comprises converting at least part of said paraffins into normally gaseous unsaturated hydrocarbons, subjecting at least part of the hydrocarbons having two to four carbon atoms per molecule in the resulting mixture to the action of sulfuric acid having a strength of from 90 to 105 per cent and a temperature within the range of to 125 F. for a time sumcient to effect union of the major part of the unsaturated hydrocarbons having three and four carbon atoms per molecule with parafilns to form hydrocarbons boiling in the gasoline range, subjecting-at least part of the unreacted hydrocarbons from the effluent having two to fourcarbon atoms per molecule to the action of thermal-alkylation conditions comprising a temperature within the range of 750 to 1100 F. and apressure in excess of about 1000 pounds per square inch for a time sufiicient for substantially all of the unsaturated hydrocarbons :having two to four carbon atoms per molecule to unite with paramns to form hydrocarbons boiling in the gasoline range, separating hydrocarbons boiling in the gasoline range from eflluents of said thermal-alkylation as products of the process, also separating and recycling at least part of the hydrocarbons efliuent from said thermalalkylation conditions and having four to seven carbon atoms to the said thermal-alkylation conditions, and returning at least part of the residual hydrocarbons having two to four carbon atoms. per molecule to the step for converting paraflins into unsaturated hydrocarbons.

4. A process of manufacturing gasoline from a feed stock comprising parafllns having two to four carbon atoms per molecule, which comprises converting at least part of said pa-raflins into normally gaseous olefin hydrocarbons, subjecting at least part of the hydrocarbons having two to four carbon atoms per molecule in the resulting mixture to the action of sulfuric acid having a strength of from 90 to 105 per cent and a temperature within the range of 0 to 125 F. for a time sufficient to eflect union of the major part of the olefin hydrocarbons having three and four carbon atoms per molecule with is-oparafllns to form hydrocarbons boiling in the gasoline range, separating hydrocarbons boiling in the gasoline range from eflluents of said alkylation as products of the process, also separating and recycling at least part of the hydrocarbons having four to seven carbon atoms per molecule to the action of sulfuric acid, subjecting at least part of the unreacted hydrocarbons having two to four carbon atoms per molecule to the action of thermalalkylation conditions comprising a temperature within the range of 750 to 1100 F. and a pressure in excess of about 1000 pounds per square inch for a time sumcient for substantia ly all of the olefin hydrocarbons having two to tour carbon atoms per molecule to unite with paraflins to form hydrocarbons boiling in the gasoline range, and returning at least part of the residual hydrocarbons having two to four carbon atoms per molecule to the step for converting parafiins into olefin hydrocarbons.

5. In the process of claim 4 recycling at least, part of the hydrocarbons effluent from said thermal-alkylation conditions and having four to seven carbon atoms per molecule to the said thermal-alkylation conditions.

6. A process for producing normally liquid hydrocarbons in the motor fuel boiling range from lower boiling hydrocarbons, which comprises subjecting a hydrocarbon mixture containing ethylene and heavier olefin hydrocarbons and also propane and heavier parafiin hydrocarbons to a first set of conditions favoring union of olefin hydrocarbons heavier than ethylene with paraffin hydrocarbons to produce normally liquid hydrocarbons in the motor fuel boiling range, separating from the efiiuent a fraction comprising ethylene and parafiin hydrocarbons having two to seven carbon atoms per molecule, subjecting said 1 fraction to a second and more drastic set of alkylation conditions favoring union of ethylene with at least a part of the parafiln hydrocarbons having two to seven carbon atoms per molecule to form hydrocarbons in the gasoline boiling range, separating from the effluent a fraction comprising hydrocarbons in the gasoline boiling range so produced, andv also separating from said effluent a hydrocarbon fraction containing normally liquid hydrocarbons of not more than seven carbon atoms per molecule and returning said fraction to said second alkylation step.

'7. A process of manufacturing gasoline from a feed stock comprising parafiins having two to four carbon atoms per molecule which comprises converting at least a part of sa d parafflns into normally gaseous unsaturated hydrocarbons. subiecting a resulting hydrocarbon fraction containing paraflln and unsaturated hydrocarbons having two to four carbon atoms per molecule to the action of an alkylation catalyst under alkylation conditions such as to effect union of the major part of the unsaturated hydrocarbons having three and four carbon atoms per molecule with parafiins to form hydrocarbons in the gasoline boiling range. se arating from the effluent a hydrocarbon fraction boiling in the gasoline range and of a low volatility, separating also a low-boiling fraction comprising ethylene and paraffin hydrocarbons having two to seven carbon atoms per atoms per molecule and returning same to said thermal-alkylation conditions. and blendin said low volatile fraction and sa d hi hly volatile fraction to produce a composite fraction boiling in the gasoline range.

FREDERICK E. FREY. 

